Ductless electric induction furnace and process for the starting thereof



June 10, 1958 G. A. TAGLIAFERR] 2,838,588

DUCTLESS ELECTRIC INDUCTION FURNACE AND PROCESS FOR THE STARTING THEREOF Filed July 12, 1955 IN V EN TOR.

United States Patent Ofiiice DUCTLESS ELECTRIC INDUCTION FURNACE AND PROCESS FOR THE STARTING THEREOF Giacomo Aldo Tagliaferri, Milan, Italy Application July 12, 1955, Serial No. 521,563 Claims priority, application Great Britain July 15, 1954 4 Claims. (Cl. 13-28) This invention relates to an electric induction furnace and a process for the cold starting thereof.

It is known that when an induction furnace has to be extinguished, considerable difliculties are encountered when resuming the firing, and in the preservation of the clay work.

The same is true when it is desired to change the material to be cast, for example from ferrous to non-ferrous metals, without replacing the clay work, and without resorting to a special cleaning of the furnace ducts.

This situation has led, in several cases, to the adoption of ductless furnaces, both low and high-frequency types. These furnaces, however, have a rather low operating power factor, and therefore require the use of many re-phasing condensers if they are to operate without requiring excessively high inputs. This solution however, is so expensive as in many cases to be undesirable.

An object of this invention is the provision of an electric induction furnace, wherein the inductor system is still a ring, but said ring is widened to form a wide basin, making it similar to a conventional crucible. It is thus possible to provide an operation entirely similar to that of ductless furnaces, and at the same time to dispense with the use of several condensers, since the power factor of the furnace of the invention ranges between .8 and .6, depending on the metals and/or alloys to be cast.

While it frequently happens, particularly in casting aluminum or aluminum alloys, that the ring ducts tend to become clogged because of the tendency of metal oxides to stick to the fireclay wall, and it becomes necessary to scrape the walls of the ducts at frequent intert vals; in the furnace proposed by the present invention the operation is much easier and simpler. 7

Another advantage of the invention is that, since all the furnace walls are accessible, the clay work can be easily repaired.

The invention will be described further ample with reference to the which:

Fig. 1 is a longitudinal section along a central plane through a furnace constructed in accordance with the in vention, and

Fig. 2 is a plan view of the furnace, partly in cross section.

With reference to the drawings, the furnace is characterized by an annular chamber 1- which, when the furnace is fired, contains the first active element to start the melting process. On the front side, this chamber widens to form a large crucible 2 which is directly accessible from all sides after removal of the upper core armature 3 and lid 4. Thus it is always possible, when preparing the furnace for operation, to introduce a ring of the same metal or alloy which is to be melted.

Another characteristic of the furnace according to the invention is that the part of the furnace upon which is placed a fireclay plate 6 and which contains the housing for the said melting ring, can be easily opened and is located very near to the magnetic core from which it by way of exaccompanying drawings, in

2,838,588 Patented June 10, 1958 is separated only by a small thickness of fire clay. The fire clay is cooled by an inverted-flow copper pipe coil 7, 8. This coil has a twofold function, because it also carries the current of the primary heating circuit.

To empty the furnace, at pouring spout 9 and a nozzle 10 are provided.

The shape of ring 1 can be circular, elliptical or even polygonal.

-Various changes and modifications may be made without departing from the spirit and scope of the present invention and it is intended that such obvious changes and modifications be embraced by the annexed claims.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent, is:

1. An induction furnace, comprising a receptacle of refractory material for receiving a substance to be melted, said receptacle having a center, a closed bottom and an open top and being provided in its interior with a hollow, thin-walled, eccentrically disposed column of said refractory material, said column having a lower part and an upper part and extending from said bottom to said top of said receptacle, said bottom being provided with an annular groove surrounding said lower part of said column and communicating with the remainder of said receptacle interior, said remainder of said receptacle interior surrounding said upper part of said column and extending to one side of said annular groove and of said column past said center of said receptacle, hollow electrically conductive coil means defining both a flow path for a cooling medium and an electric alternating current circuit and arranged for connection to a source of A. C. electric power, a portion of said coil means being located within the interior of said column, another portion of said coil means being located beneath said bottom of said receptacle and concentrically with respect to said groove, and rectangular magnetic core means for said coil means, said core means comprising a U-shaped yoke having parallel legs and a bridging portion fixedly connected to said legs at respective first end portions of the latter, and an armature releasably connected to and bridging respective second end portions of said legs, one of said legs extending substantially centrally through said column and said coil means, whereby the gap between said one leg of said magnetic core means and said groove is reduced to a minimum to facilitate, upon flow of alternating electric current through said coil means, melting of an initial annular solid charge of said substance when the latter is located in said groove.

2. An induction furnace, comprising a receptacle of refractory material for receiving a substance to be melted, said receptacle having a closed bottom and an open top, a hollow, thin-walled column of said refractory material disposed eccentrically within the interior of said recep tacle, said column having a lower part and an upper part and extending from said bottom to said top of said receptacle, said bottom being provided with a narrow annular groove extending around said lower part of said column substantially concentrically therewith, the remainder of said receptacle interior being wider than said groove and surrounding said upper part of said column and communicating with said annular groove, 21 major portion of said remainder of said receptacle interior being disposed to one side of said column and said groove, hollow electrically conductive coil means defining a flow path for a cooling medium and further an alternating current circuit arranged for connection to a source of A. C. power, a portion of said coil means being located within the interior of said column, another portion of said coil means being located beneath said bottom of said receptacle and concentrically with respect to said groove, magnetic core means for said coil means, said core means comprising a U-shaped yoke having spaced legs and a bridging por- 2,sas,ses 7 7 tion'fixedly connected to bothsaid legs at respective first end portions of the latter, and an armature vreleasably connected to respective second end portions of said legs and bridging the gap therebetween, one of said legs extending substantially centrally through. said column and said coil means, and a cover for said receptacle, said cover resting on said column intermediate said upper part of the latter and said armature and being providedwith an apertureregistrable with said interior of said column for passage of said one leg of said core means through said aperture, said cover thereby being retained on said. column by said armature, the space between said one leg of said magnetic core means and said groove being reduced to a minimum by the thinness of said wall of said column to facilitate melting, upon how of electric'current through said coil means, of an initial solid charge of said substance when the latter is located in said groove.

3. The process of cold starting a low-frequency induction furnace for use in connection With melting of metals, alloys and like substances, comprising the steps of placing an annular solid mass of the substance to be melted in an annular chamber of narrow cross-section adjacent the bottom of said furnace, placing any additional'amount of said substance in another Wider chamber located above and eccentrically with respect to said annular chamber and merging with said annular chamber, generating a low-frequency alternating current-produced magnetic nfieldtat a. location-at least partly-centrally of said annular mass in said annular chamber, and applying said magnetic field at least to said annular mass to cause generation of heat therein sufficient to melt the same.

4. An induction furnace, comprising means defining a first annular chamber of symmetrical shape and restricted width and a second annular chamber of asymmetricalxshape; andjof greater width than said first annular chamber, Jsecond annular'chamber being located eccentrically-a ove and communicating with said-first annular chamber, means having a part located centrally of said first annular chamber for generating an alternating magnetic fieldto be applied to a substance to be melted when in said first and second chambers, a lid for said second annular chamber, and means constituting a further part of said field-generating means for releasably retaining both the latter and said lid in operative position relative to saidchambers.

References Cited inthe file of this patent UNITED STATES PATENTS 962,0l3 Dc Perranti June 21, l9l0 1,564,800 Unger Dec. 8, 1925 1,937,065 Moore Nov. 28, 1933 

